Co-owned U.S. Pat. No. 4,385,728 discloses a flow-amplifying nozzle having a tapered nose section over which a high velocity film of primary air is directed. Secondary air is entrained by the rapid flow of primary air and thereby amplifies the total flow of air directed by the nozzle. Another U.S. Pat. No. 4,195,780 discloses an external-flow nozzle that operates on the same principle but which also includes an annular metering passage that is adjustable for varying the flow of primary air from the nozzle.
The prior art is replete with designs for nozzles capable of spraying or atomizing liquids. Those nozzles that utilize pressurized air might be regarded as falling into three broad categories, namely, those that operate on a flit gun principle, those that mix liquid and air internally, and those which generate shock waves to produce atomization and are commonly referred to as sonic nozzles.
In the flit gun type of nozzle, pressurized air strips liquid from the end of a feed tube that usually extends at right angles to the tip of the nozzle just beyond its outlet. Since the intermixing of liquid and air occurs externally and, especially since the feed tube opening is usually relatively large, problems of clogging are minimized. However, directivity is ordinarily lacking. Such a construction is commonly used for fogging where the need for directivity is minimal, although patents such as U.S. Pat. No. 1,326,483 reveal that the same principle of operation has been employed in paint spraying devices.
Sprayers for applying liquid coatings are sometimes designed to intermix the liquid and air internally, prior to discharge from the nozzle. Such an arrangement promotes directivity but with offsetting disadvantages such as a greater likelihood of clogging. Also, achieving uniform liquid particle size may be more difficult, especially if such particles impact and cling to internal surfaces near the outlet of the nozzle where they agglomerate or reclassify and are then discharged randomly as relatively large droplets. Reference may be had to patents disclosing paint sprayers and air brushes such as U.S. Pat. Nos. 1,603,902, 1,294,190, 1,218,279, and 3,796,376.
Accordingly, it is an object of this invention to provide a liquid-atomizing nozzle that has the directivity needed for spraying liquid coatings (but, if desired, may be constructed to provide low directivity for uses such as fogging, humidifying, and suppressing or controlling dust); is relatively simple and inexpensive in construction; is highly effective in achieving uniformity of liquid particle size and, specifically, avoids problems of particle reclassification and droplet formation; and is relatively quiet in operation. When adapted for fogging or humidifying, the nozzle is well suited for discharging liquid particles so small that such particles will flash into vapor less than 30 inches from the end of the nozzle. In short, this invention is directed to a nozzle which has important advantages of various types of prior nozzles without the significant disadvantages associated with the earlier constructions.
Briefly, the liquid-atomizing nozzle includes a tubular body having a generally cylindrical section with an axial bore and a conical, inwardly-tapered nose section projecting from one end of the cylindrical section. The nose section has liquid outlet means for externally discharging liquid from that section. In one form of the invention, the outlet means comprises an axial discharge opening at the tip of the nose section; in another form, such means comprises a plurality of circumferentially-spaced discharge openings about the conical surface of the nose section. In either case, the outlet means communicates with a liquid supply conduit extending through the bore of the tubular body.
The nozzle is provided with an annular collar that extends about the cylindrical section of the body and has a flow-directing section and an attachment section. The flow-directing section of the collar has a bore sufficiently greater in diameter than the outside of the cylindrical section to define an annular flow-directing passage that communicates with a multiplicity of openings extending through the wall of the body's cylindrical section. The flow-directing passage faces towards the nose section for directing a stream or curtain of high-velocity primary air along the conical surface of the nose section. As the high velocity air flows over the surface of the gradually tapered nose (the taper should not exceed about 25.degree. measured from the longitudinal axis), the primary air entrains surrounding secondary air which amplifies the total flow and also reduces operating noise. As the high-velocity primary air travels past the liquid outlet or outlets, it strips away the liquid and atomizes into particles of selected size, such size being dependent partly on the pressure and velocity of the primary air, the location and size of the liquid discharge outlet(s), and the pressurization (if any) of the liquid medium.
In the embodiment in which the liquid outlet takes the form of an opening at the tapered distal end of the nose section, the surface of the outlet means immediately adjacent that opening flares outwardly and distally, merging with the tapered outer surface of the nose section in a circular terminal edge. Liquid flows outwardly along the flared surface and is stripped away by the primary air at the point where that surface converges with the conical outer surface of the nose.
The second embodiment, in which the liquid outlet means takes the form of a plurality of discharge openings arranged in a circumferentially-spaced series about the conical surface at the proximal end of the nose section, is particularly suitable for producing the extremely small liquid particle sizes required for suppressing dust, humidifying, and fogging.
Other features, objects, and advantages will become apparent from the specification and drawings.